Letter pubs.acs.org/acsmedchemlett
Triazolylthioacetamide: A Valid Scaffold for the Development of New Delhi Metallo-β-Lactmase‑1 (NDM-1) Inhibitors Le Zhai,†,‡,⊥ Yi-Lin Zhang,†,⊥ Joon S. Kang,§ Peter Oelschlaeger,∥ Lin Xiao,† Sha-Sha Nie,† and Ke-Wu Yang*,† †
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710127, P. R. China ‡ College of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji 721016, P. R. China § Department of Biological Sciences, California State Polytechnic University, 3801 West Temple Avenue, Pomona, California 91768, United States ∥ Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, 309 East Second Street, Pomona, California 91766, United States S Supporting Information *
ABSTRACT: The metallo-β-lactamases (MβLs) cleave the β-lactam ring of β-lactam antibiotics, conferring resistance against these drugs to bacteria. Twenty-four triazolylthioacetamides were prepared and evaluated as inhibitors of representatives of the three subclasses of MβLs. All these compounds exhibited specific inhibitory activity against NDM-1 with an IC50 value range of 0.15−1.90 μM, but no activity against CcrA, ImiS, and L1 at inhibitor concentrations of up to 10 μM. Compounds 4d and 6c are partially mixed inhibitors with Ki values of 0.49 and 0.63 μM using cefazolin as the substrate. Structure−activity relationship studies reveal that replacement of hydrogen on the aromatic ring by chlorine, heteroatoms, or alkyl groups can affect bioactivity, while leaving the aromatic ring of the triazolylthiols unmodified maintains the inhibitory potency. Docking studies reveal that the typical potent inhibitors of NDM-1, 4d and 6c, form stable interactions in the active site of NDM-1, with the triazole bridging Zn1 and Zn2, and the amide interacting with Lys 211 (Lys224). KEYWORDS: Metallo-β-lactamase, NDM-1, triazolylthioacetamide, inhibitor enzymes utilize either 1 or 2 equiv of Zn(II) to catalyze the βlactam hydrolysis reaction.6−8 MβLs are able to promote the hydrolysis of a broad range of β-lactam antibiotics, including penicillins, cephalosporins, and carbapenems.9 MβLs are further divided into subclasses B1−B3, based on amino acid sequence homologies and Zn(II) content.10 New Delhi metallo-β-lactmase-1 (NDM-1), a B1 subclass enzyme first discovered in 2008,11 has become a global threat because it confers resistance to almost all β-lactam antibiotics and due to its rapid spread of the plasmid-encoded NDM-1 gene.12,13
T
he emergence of antibiotic resistance is a global challenge for public health. To withstand β-lactam antibiotics, large numbers of pathogenic bacteria have evolved resistance. During the past decade, prevalence of antibiotic-resistant pathogens harboring mechanisms, such as reduced cell-wall permeability, efflux of antibiotics, and drug degradation mediated by βlactamases, has become a major concern worldwide.1−4 βLactamases are enzymes that decompose β-lactam antibiotics by hydrolyzing the C−N bond of their β-lactam ring. According to the Ambler convention, β-lactamases are grouped into four classes, A−D, based on their amino acid sequence homologies.5 Class A, C, and D enzymes comprise the serine β-lactamases, which utilize an active-site serine as a nucleophile. Class B enzymes are called metallo-β-lactamases (MβLs), and these © XXXX American Chemical Society
Received: December 23, 2015 Accepted: February 16, 2016
A
DOI: 10.1021/acsmedchemlett.5b00495 ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX
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The inhibitors of serine-β-lactamases (classes A, C, and D), such as tazobactam and sulbactam, have been used in combination with penicillins to treat infections with resistant bacteria. Novel effective MβL inhibitors for such combination therapies are urgently needed.14−16 Marchand-Brynaert et al. reported a series of mercaptoacetic acid thiol ester derivatives as potent MβL inhibitors, which provided a starting point for the design of sulfur-doped “pro-inhibitors”.17 Subsequently, other sulfur-containing compounds, such as thiol carboxylates,18 thiols,19,20 and thiomandelic acid,21 were synthesized and evaluated. Thiomandelic acid was reported to be a broadspectrum inhibitor of MβLs with Ki values of 0.09 μM for Rthiomandelic acid and 1.28 μM for the S-isomer. Moreover, NMR assays pointed out that the thiol group of both R- and Sthiomandelic acids was capable of binding to the two zinc ions in the active site.21 Faridoon et al. reported that 3-mercapto1,2,4-triazoles and N-acylated thiosemicarbazides exhibited moderate inhibitory activity against the MβL IMP-1 from Pseudomonas aeruginosa with a mixed inhibition mode.22 Recently, our studies showed that the azolylthioacetamide compounds specifically inhibit MβL ImiS (B2) and the most potent inhibitor exhibits an IC50 value of 70 nM.23 All tested amino acid thioester derivatives are very potent inhibitors of L1 (B3), exhibiting an IC50 value range of 0.018−2.9 μM.24 These thiol esters can release mercaptoacetic acid, which may form a disulfide bond to the active-site cysteine residue or coordinate Zn(II), thereby inactivating the enzyme.17 N-Heterocyclic dicarboxylic acids are inhibitors of MβLs;25 and the diarylsubstituted azolylthioacetamides exhibit broad-spectrum inhibitory activity against the MβLs L1, ImiS, and NDM-1 (B1).26 The information gained in our previous studies suggests that the triazolylthioacetamide is a valid scaffold for the development of NDM-1 inhibitors. Therefore, in this work a series of triazolylthioacetamides (shown in Figure 1) were synthesized, characterized, and evaluated against MβLs.
Scheme 1. Synthetic Route of Triazolylthioacetamides
benzoylhydrazines reacted with NH4SCN under acid conditions to give correlative aroylthioureas (s4), which were converted into the substituted triazolylthiols (a−d) at reflux in the presence of sodium hydroxide. Finally, the target triazolylthioacetamides were generated by a nucleophilic substitution reaction under alkaline conditions.27 To test whether these triazolylthioacetamides were specific or even broad-spectrum inhibitors of the MβLs, MβLs from subclasses B1a (CcrA), B1b (NDM-1), B2 (ImiS), and B3 (L1) were overexpressed and purified as previously described.28−31 In vitro, the inhibitory activities of all compounds prepared were tested against the MβLs on an Agilent UV8453 spectrometer as described by Bush et al., using cefazolin (imipenem for ImiS) as the substrate.32 The substrate concentrations were varied between 26 and 160 μM, and inhibitor concentrations were varied between 15 nM and 10 μM. Enzyme and inhibitor were preincubated for 60 min before starting the kinetic experiments. The inhibitor concentrations causing 50% decrease of enzyme activity (IC50) was calculated based on the kinetic data. The inhibition constants (Ki) were determined by plotting the kinetic data for slope and intercept versus substrate concentration. The inhibitory mode was identified by generating Lineweaver−Burk plots of the data. The inhibition studies indicated that the triazolylthioacetamides had specific inhibitory activity against NDM-1, but no activity was observed against CcrA, ImiS, and L1 at inhibitor concentrations of up to 10 μM. The inhibitor concentrations causing 50% decrease of enzyme activity (IC50) of triazolylthioacetamides against NDM-1 are presented in Table 1. Clearly, triazolylthioacetamides 1−6a, 1−6b, 2c, 4−6c, 1d, and 3−6d exhibited high inhibitory activities against NDM-1 with IC50 values of less than 1 μM, while 1c, 3c, and 2d showed a slightly higher IC50 value range of 1.2−1.9 μM. In particular, 1a, 4a, 2b, 4b, 4d, and 6b showed the lowest IC50 values around 0.15 μM. We previously tested the intermediates aryltriazolyl mercaptans as inhibitors of NDM-1, and the results showed that these
Figure 1. Structures of the triazolylthioacetamides.
Twenty-four triazolylthioacetamides were synthesized as shown in Scheme 1. Briefly, N-substituted 2-chloroacetamides (1−6) were first prepared by acylation between substituted anilines and chloroacetyl chloride. 5-Substituted-4H-1,2,4triazole-3-thiols (a−d) were prepared in three steps.22 Methyl arylcarboxylates (s2) were prepared by esterifying correlative substituted benzoic acids (s1) and were then converted into benzoylhydrazine (s3) by condensing with hydrazine. The B
DOI: 10.1021/acsmedchemlett.5b00495 ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX
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Table 1. IC50 Values of Triazolylthioacetamides against NDM-1 compd 1a 2a 3a 4a 5a 6a
IC50 (μM)
compd
± ± ± ± ± ±
1b 2b 3b 4b 5b 6b
0.17 0.19 0.99 0.15 0.35 0.69
0.04 0.07 0.03 0.07 0.05 0.08
IC50 (μM)
compd
IC50 (μM)
compd
IC50 (μM)
± ± ± ± ± ±
1c 2c 3c 4c 5c 6c
1.2 ± 0.1 0.98 ± 0.09 1.5 ± 0.1 0.48 ± 0.05 0.52 ± 0.03 0.37 ± 0.04
1d 2d 3d 4d 5d 6d
0.33 ± 0.05 1.9 ± 0.1 0.45 ± 0.03 0.16 ± 0.04 0.61 ± 0.02 0.23 ± 0.04
0.42 0.16 0.93 0.16 0.98 0.16
0.07 0.05 0.08 0.03 0.06 0.02
intermediates have no inhibitory activity against the enzyme. Within this series of new inhibitors, comparison of their potencies reveals that in the presence of the triazole ring, most substitutions did not alter their potency against NDM-1 significantly. While the hydroxyl substitution on the 4-position (1−6c) of the aromatic ring of the triazolylthiols diminishes the potency against the enzyme slightly on average, compounds with no substitution (1a, 2a, 4a, and 5a) exhibited the highest potency. Furthermore, replacement of a hydrogen at the 2position of the aromatic ring of phenylacetamide with a methyl group (2d) or an ethyl group (3a and 3b) reduces potency. Dramatically, replacing the 2-position hydrogen (1a−d) with chlorine (5a−d) does not change their activities significantly. The presence of a butyl group at the 4-position (4a−d) of the phenylacetamide increased the potency against NDM-1. Moving the chlorine from the 2- (5a−d) to the 3-position (6a−d) also had a favorable effect, except for 6a. To further identify the inhibition mode of these MβL inhibitors, typical representatives 4d and 6c were chosen to determine Ki values. Lineweaver−Burk plots of NDM-1 catalyzed hydrolysis of cefazolin in the absence and presence of inhibitors are displayed in Figure 2. Compounds 4d and 6c exhibited Ki values of 0.49 and 0.63 μM, respectively, which are slightly larger than their correlative IC50 values (0.16 and 0.37 μM, respectively). The analysis also demonstrated that both of the compounds employed the same partially mixed inhibition type. Molecular docking and its analysis (refer to Supporting Information for details) resulted in clusters of 31 and five comparable conformations (out of 50) docked into the NDM-1 active site with average binding energies of −7.2 and −8.0 kcal/ mol for 4d and 6c, respectively. The conformations displayed in Figure 3 are the lowest-energy conformations within these clusters with binding energies of −7.7 and −8.6 kcal/mol for 4d and 6c, respectively. The docking studies reveal that in compounds 4d and 6c the triazole coordinate at Zn1 and Zn2 of NDM-1 at comparable distances, which leads to nearly superimposable conformations, as can be seen in Figure 3A. In addition, they both interact with Lys211 (Lys224 according to standard numbering10) via the amide carbonyl group at distances of less than 3 Å. The hydroxyl group of compound 6c makes an additional interaction with Gln123 (Gln119), which may contribute to the almost 1 kcal/mol more favorable binding energy relative to 4d. This difference is not in agreement with experiments, though, where 4d was more potent; in reality the hydroxyl might interact with solvent instead of Gln123 (Gln119). Comparable to previous findings,23,24 the triazole ring of these compounds plays an important role in the interactions with active site Zn(II)s, while the close interaction with the conserved Lys211 (Lys224) is also observed. It was interesting to observe that the compounds had no activity against CcrA, even though the active sites of NDM-1
Figure 2. Lineweaver−Burk plot of NDM-1 catalyzed hydrolysis of cefazolin in the absence and presence of 4d (up) and 6c (down). Inhibitor concentrations were 0 μM (●), 0.25 μM (○), 0.5 μM (▼), and 1.0 μM (▽).
and CcrA are quite similar. There are two differences between the enzymes that may be significant for inhibitor binding: (1) CcrA has a glycine at position 119, which is glutamine in NDM-1 and interacts with the hydroxyl group of 6c. With glycine, no such interaction is possible in CcrA. (2) The distance between Zn2 and Lys224 is bigger in CcrA (6.8 Å)35 than in NDM-1 (5.3 Å, PDB code 4HL2). Thus, it is possible that simultaneous interaction between the triazole ring and the Zn(II) ions and between the carbonyl and Lys211 (Lys224) is more effective in NDM-1. Accordingly, docking studies with 4d and 6c to CcrA revealed that the binding energies were less favorable than in NDM-1 with mean binding energies of the corresponding and most populated clusters of −6.9 kcal/mol for both molecules. Unlike in NDM-1, there was no difference between the two molecules, which may be explained by the missing interaction between 6c and residue 119 in CcrA, and the distance between the carbonyl and Lys224 was above 3 Å in both cases, while coordination of the Zn(II) ions by the triazole ring was maintained. Combined, these observations argue that Lys211 (Lys224) cannot be too distant from the Zn(II) ions for effective inhibitor binding. C
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triazolylthiols unmodified resulted in highest potency of the compounds. The work presented here has identified 24 potential partially mixed inhibitors for inhibition studies on NDM-1. Docking studies reveal that 4d and 6c, as typical potent NDM-1 inhibitors, form stable interactions in the active site of NDM-1, with the triazole bridging Zn1 and Zn2, and the amide interacting tightly with Lys211 (Lys224).
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmedchemlett.5b00495. Detailed synthesis procedure, NMR and ESI mass data for all target compounds, the methods for enzyme expression and purification, assay of inhibitory activity, and docking study (PDF)
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AUTHOR INFORMATION
Corresponding Author
*Tel/Fax: +8629-8153-5035. E-mail:
[email protected]. Author Contributions ⊥
These authors contributed equally to this work. The manuscript was written through contributions of all authors. Funding
This work was supported by grants 81361138018, 21272186, and 21572179 (to K.W.Y.) from the National Natural Science Foundation of China. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Blair, J. M.; Webber, M. A.; Baylay, A. J.; Ogbolu, D. O.; Piddock, L. J. Molecular mechanisms of antibiotic resistance. Nat. Rev. Microbiol. 2015, 13, 42−51. (2) Tang, S. S.; Apisarnthanarak, A.; Hsu, L. Y. Mechanisms of βlactam antimicrobial resistance and epidemiology of major community- and healthcare-associated multidrug-resistant bacteria. Adv. Drug Delivery Rev. 2014, 78, 3−13. (3) Hawkey, P. M. Multidrug-resistant Gram-negative bacteria: a product of globalization. J. Hosp. Infect.. 2015, 89, 241−7. (4) Zavascki, A. P.; Bulitta, J. B.; Landersdorfer, C. B. Combination therapy for carbapenem-resistant Gram-negative bacteria. Expert Rev. Anti-Infect. Ther. 2013, 11, 1333−53. (5) (a) Bush, K.; Jacoby, G. A. Updated functional classification of beta-lactamases. Antimicrob. Agents Chemother. 2010, 54, 969−76. (b) Bush, K. The ABCD’s of β-lactamase nomenclature. J. Infect. Chemother. 2013, 19, 549−59. (6) Bush, K. The ABCD’s of β-lactamase nomenclature. J. Infect. Chemother. 2013, 19, 549−59. (7) Karsisiotis, A. I.; Damblon, C. F.; Roberts, G. C. A variety of roles for versatile zinc in metallo-βeta-lactamases. Metallomics. 2014, 6, 1181−97. (8) Meini, M. R.; Llarrull, L. I.; Vila, A. J. Overcoming differences: The catalytic mechanism of metallo-β-lactamases. FEBS Lett. 2015, 589, 3419−32. (9) Crowder, M. W.; Spencer, J.; Vila, A. J. Metallo-β-lactamases: novel weaponry for antibiotic resistance in bacteria. Acc. Chem. Res. 2006, 39, 721−8. (10) Galleni, M.; Lamotte-Brasseur, J.; Rossolini, G. M.; Spencer, J.; Dideberg, O.; Frere, J. M. Standard numbering scheme for class B βlactamases. Antimicrob. Agents Chemother. 2001, 45, 660−3. (11) Yong, D.; Toleman, M. A.; Giske, C. G.; Cho, H. S.; Sundman, K.; Lee, K.; Walsh, T. R. Characterization of a new metallo-β-lactamase
Figure 3. Low energy conformations of 4d and 6c docked into the active site of NDM-1 (PDB code 4HL233). The enzyme backbone is shown as cartoon in green, and selected residue side chains are shown as sticks colored by atom (C, cyan; N, blue; O, red; S, yellow). The Zn(II) ions are shown as purple spheres. (A) Superimposition of compounds 4d and 6c in the NDM-1 active site. Compound 6c is depicted as sticks colored by atom (same colors as for protein residues except C in gray), and 4d as yellow sticks. (B,C) Detailed views of 4d and 6c, respectively, displaying key enzyme residues and indicating interactions between the inhibitors and enzyme residues with dashed lines. Panels A−C were generated with VMD.34
In summary, 24 triazolylthioacetamides were synthesized and a general method was devised to develop various triazolylthioacetamides as MβL inhibitors. In vitro biological activity assay revealed that the triazolylthioacetamides displayed partially mixed inhibition activity against NDM-1, with an IC50 values range of 0.15−1.90 μM. The analysis of the structure−activity relationship reveals that replacement of hydrogen on the aromatic ring by either chlorine or alkyl group can apparently have bioactivity consequences and suggests that the 4-position of the phenylacetamide plays a more significant role than the 2position. Moreover, leaving the aromatic ring of the D
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provides multiple antibiotic resistance. J. Biol. Chem. 1998, 273, 22402−8. (29) Yang, H.; Aitha, M.; Hetrick, A. M.; Richmond, T. K.; Tierney, D. L.; Crowder, M. W. Mechanistic and spectroscopic studies of metallo-β-lactamase NDM-1. Biochemistry 2012, 51, 3839−47. (30) Crawford, P. A.; Sharma, N.; Chandrasekar, S.; Sigdel, T.; Walsh, T. R.; Spencer, J.; Crowder, M. W. Over-expression, purification, and characterization of metallo-β-lactamase ImiS from Aeromonas veronii bv. sobria. Protein Expression Purif. 2004, 36, 272−9. (31) Crowder, M. W.; Walsh, T. R.; Banovic, L.; Pettit, M.; Spencer, J. Overexpression, purification, and characterization of the cloned metallo-β-lactamase L1 from Stenotrophomonas maltophilia. Antimicrob. Agents Chemother. 1998, 42, 921−6. (32) Bush, K.; Macalintal, C.; Rasmussen, B. A.; Lee, V. J.; Yang, Y. Kinetic interactions of Tazobactam with β-lactamases from all major structural classes. Antimicrob. Agents Chemother. 1993, 37, 851−8. (33) Kim, Y.; Tesar, C.; Mire, J.; Jedrzejczak, R.; Binkowski, A.; Babnigg, G.; Sacchettini, J.; Joachimiak, A. Structure of apo- and monometalated forms of NDM-1–a highly potent carbapenemhydrolyzing metallo-β-lactamase. PLoS One 2011, 6, e24621. (34) Humphrey, W.; Dalke, A.; Schulten, K. VMD: visual molecular dynamics. J. Mol. Graphics 1996, 14 (33−8), 27−8. (35) Fitzgerald, P. M.; Wu, J. K.; Toney, J. H. Unanticipated inhibition of the metallo-b-lactamase from Bacteroides f ragilis by 4morpholineethanesulfonic acid (MES): a crystallographic study at 1.85 Å resolution. Biochemistry 1998, 37, 6791−800.
gene, bla(NDM-1), and a novel erythromycin esterase gene carried on a unique genetic structure in Klebsiella pneumoniae sequence type 14 from India. Antimicrob. Agents Chemother. 2009, 53, 5046−54. (12) Liang, Z.; Li, L.; Wang, Y.; Chen, L.; Kong, X.; Hong, Y.; Lan, L.; Zheng, M.; Guang-Yang, C.; Liu, H.; Shen, X.; Luo, C.; Li, K. K.; Chen, K.; Jiang, H. Molecular basis of NDM-1, a new antibiotic resistance determinant. PLoS One 2011, 6, e23606. (13) Yang, H.; Aitha, M.; Hetrick, A. M.; Richmond, T. K.; Tierney, D. L.; Crowder, M. W. Mechanistic and spectroscopic studies of metallo-β-lactamase NDM-1. Biochemistry 2012, 51, 3839−47. (14) Toney, J. H.; Moloughney, J. G. Metallo-β-lactamase inhibitors: promise for the future? Curr. Opin. Investig. Drugs 2004, 5, 823−6. (15) Drawz, S. M.; Bonomo, R. A. Three decades of β-lactamase inhibitors. Clin. Microbiol. Rev. 2010, 23, 160−201. (16) Guo, Z.; Ma, S. Recent advances in the discovery of metallo-βlactamase inhibitors for β-lactam antibiotic-resistant reversing agents. Curr. Drug Targets 2014, 15, 689−702. (17) Payne, D. J.; Bateson, J. H.; Gasson, B. C.; Proctor, D.; Khushi, T.; Farmer, T. H.; Tolson, D. A.; Bell, D.; Skett, P. W.; Marshall, A. C.; Reid, R.; Ghosez, L.; Combret, Y.; Marchand-Brynaert, J. Inhibition of metallo-β-lactamases by a series of mercaptoacetic acid thiol ester derivatives. Antimicrob. Agents Chemother. 1997, 41, 135−40. (18) Concha, N. O.; Janson, C. A.; Rowling, P.; Pearson, S.; Cheever, C. A.; Clarke, B. P.; Lewis, C.; Galleni, M.; Frere, J. M.; Payne, D. J.; Bateson, J. H.; Abdel-Meguid, S. S. Crystal structure of the IMP-1 metallo β-lactamase from Pseudomonas aeruginosa and its complex with a mercaptocarboxylate inhibitor: binding determinants of a potent, broad-spectrum inhibitor. Biochemistry 2000, 39, 4288−98. (19) Siemann, S.; Clarke, A. J.; Viswanatha, T.; Dmitrienko, G. I. Thiols as classical and llow-binding inhibitors of IMP-1 and other binuclear metallo-β-lactamases. Biochemistry 2003, 42, 1673−83. (20) Lienard, B. M.; Garau, G.; Horsfall, L.; Karsisiotis, A. I.; Damblon, C.; Lassaux, P.; Papamicael, C.; Roberts, G. C.; Galleni, M.; Dideberg, O.; Frere, J. M.; Schofield, C. J. Structural basis for the broad-spectrum inhibition of metallo-β-lactamases by thiol. Org. Biomol. Chem. 2008, 6, 2282−94. (21) Mollard, C.; Moali, C.; Papamicael, C.; Damblon, C.; Vessilier, S.; Amicosante, G.; Schofield, C. J.; Galleni, M.; Frere, J. M.; Roberts, G. C. Thiomandelic acid, a broad spectrum inhibitor of Zinc βlactamases: kinetic and spectroscopic studies. J. Biol. Chem. 2001, 276, 45015−23. (22) Faridoon; Hussein, W. M.; Vella, P.; Islam, N. U.; Ollis, D. L.; Schenk, G.; McGeary, R. P. 3-Mercapto-1,2,4-triazoles and N-acylated thiosemicarbazides as metallo-β-lactamase inhibitors. Bioorg. Med. Chem. Lett. 2012, 22, 380−6. (23) Yang, S. K.; Kang, J. S.; Oelschlaeger, P.; Yang, K. W. Azolylthioacetamide: a highly promising scaffold for the development of metallo-β-lactamase inhibitors. ACS Med. Chem. Lett. 2015, 6, 455− 60. (24) Liu, X. L.; Shi, Y.; Kang, J. S.; Oelschlaeger, P.; Yang, K. W. Amino acid thioester derivatives: a highly promising scaffold for the development of metallo-β-lactamase L1 inhibitors. ACS Med. Chem. Lett. 2015, 6, 660−4. (25) Feng, L.; Yang, K. W.; Zhou, L. S.; Xiao, J. M.; Yang, X.; Zhai, L.; Zhang, Y. L.; Crowder, M. W. N-heterocyclic dicarboxylic acids: broad-spectrum inhibitors of metallo-β-lactamases with co-antibacterial effect against antibiotic-resistant bacteria. Bioorg. Med. Chem. Lett. 2012, 22, 5185−9. (26) Zhang, Y. L.; Yang, K. W.; Zhou, Y. J.; LaCuran, A. E.; Oelschlaeger, P.; Crowder, M. W. Diaryl-Substituted Azolylthioacetamides: Inhibitor Discovery of New Delhi Metallo-β-Lactamase1(NDM-1). ChemMedChem 2014, 9, 2445−8. (27) Patel, R. V.; Patel, P. K.; Kumari, P.; Rajani, D. P.; Chikhalia, K. H. Synthesis of benzimidazolyl-1,3,4-oxadiazol-2ylthio-N-phenyl (benzothiazolyl) acetamides as antibacterial, antifungal and antituberculosis agents. Eur. J. Med. Chem. 2012, 53, 41−51. (28) Wang, Z.; Benkovic, S. J. Purification, characterization, and kinetic studies of a soluble Bacteroides f ragilis metallo-β-lactamase that E
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